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<title>Iterator Traits</title>
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<h1 class="title">Iterator Traits</h1>
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<tr><th class="docinfo-name">Author:</th>
<td>David Abrahams</td></tr>
<tr><th class="docinfo-name">Contact:</th>
<td><a class="first last reference external" href="mailto:dave&#64;boost-consulting.com">dave&#64;boost-consulting.com</a></td></tr>
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<td><a class="first last reference external" href="http://www.boost-consulting.com">Boost Consulting</a></td></tr>
<tr><th class="docinfo-name">Date:</th>
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<td>Copyright David Abrahams 2004.</td></tr>
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<tr class="field"><th class="field-name">abstract:</th><td class="field-body">Header <tt class="docutils literal">&lt;boost/iterator/iterator_traits.hpp&gt;</tt> provides
the ability to access an iterator's associated types using
MPL-compatible <a class="reference external" href="../../mpl/doc/index.html#metafunctions">metafunctions</a>.</td>
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<div class="section" id="overview">
<h1>Overview</h1>
<p><tt class="docutils literal"><span class="pre">std::iterator_traits</span></tt> provides access to five associated types
of any iterator: its <tt class="docutils literal">value_type</tt>, <tt class="docutils literal">reference</tt>, <tt class="docutils literal">pointer</tt>,
<tt class="docutils literal">iterator_category</tt>, and <tt class="docutils literal">difference_type</tt>.  Unfortunately,
such a &quot;multi-valued&quot; traits template can be difficult to use in a
metaprogramming context.  <tt class="docutils literal">&lt;boost/iterator/iterator_traits.hpp&gt;</tt>
provides access to these types using a standard <a class="reference external" href="../../mpl/doc/index.html#metafunctions">metafunctions</a>.</p>
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<div class="section" id="summary">
<h1>Summary</h1>
<p>Header <tt class="docutils literal">&lt;boost/iterator/iterator_traits.hpp&gt;</tt>:</p>
<pre class="literal-block">
template &lt;class Iterator&gt;
struct iterator_value
{
    typedef typename
      std::iterator_traits&lt;Iterator&gt;::value_type
    type;
};

template &lt;class Iterator&gt;
struct iterator_reference
{
    typedef typename
      std::iterator_traits&lt;Iterator&gt;::reference
    type;
};


template &lt;class Iterator&gt;
struct iterator_pointer
{
    typedef typename
      std::iterator_traits&lt;Iterator&gt;::pointer
    type;
};

template &lt;class Iterator&gt;
struct iterator_difference
{
    typedef typename
      detail::iterator_traits&lt;Iterator&gt;::difference_type
    type;
};

template &lt;class Iterator&gt;
struct iterator_category
{
    typedef typename
      detail::iterator_traits&lt;Iterator&gt;::iterator_category
    type;
};
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